Here is a write up on replacing cv boots.
http://www.4x4wire.com/isuzu/tech/CVboots/
If they are freshly broken you can probably clean and regrease them and just put on new boot. If they have been broken for a while or you dont know how long its been like that then the shafts should be replaced. Same procedure to replace the shafts as replacing the boots. Its best to get isuzu OEM shafts as they are stronger then aftermarket and you can replace just the shaft without the inner axle cup (major work involved in replacing that). Should be able to find plenty of good shafts in salvage yards. As long as the boots are in tact they should be fine, just put new boots on them.